Direct current (DC) energy sources, such as batteries, are used in many situations where constant alternating current (AC) power is not available (e.g., within a vehicle). In many applications, it is desirable or even critical to monitor the charge level of the energy source so that a user has an indication when an energy source is getting low on voltage or is deviating from a desired voltage range, and needs to be recharged or replaced. The voltage level on the energy source is a measurable indicator of charge of the energy source, and can be monitored with a device commonly known as a “monitor” or a “battery monitor” where the source is a battery. Without a monitor, typically the only inherent indication that a user has that the energy source is in a charged state is whether or not it activates the equipment to which it is attached. Many conventional devices exist which measure the voltage level on a battery or other DC energy source and display the charge level through some means (e.g., bar graph, digit readout, mechanical meter).
However, these devices generally lack of accuracy, particularly, when a variety of loads being applied to the battery. Some devices require that the battery being in a “rest” state (e.g., idle for a period of time without any load being applied), in order to obtain certain level of accuracy. However, such as ideal state would not be practical in real life. Better solutions are needed.